Log Message:
oniguruma: updated to 6.9.6rc1

Add handling of -revN as plN (instead of .N) and -rcN as rcN in Makefile.
Use the -revN or -rcN naming in DISTFILE, as they are (apparently) created
automatically by GitHub. Munge GITHUB_RELEASE to produce the tag name with
an underscore instead of a hyphen before rev or rc. Munge WRKSRC to strip
both -revN and -rcN.

6.9.6 Release Candidate 1
- In a Unix environment, if you have the POSIX API enabled in
  an earlier version (disabled by default in 6.9.5) and you
  need application binary compatibility with the POSIX API,
  specify "--enable-binary-compatible-posix-api=yes" instead of
  "--enable-posix-api=yes". "--enable-posix-api=yes" only \ 
supports
  source-level compatibility for POSIX API since 6.9.6.
- NEW: configure option --enable-binary-compatible-posix-api=[yes/no]
- NEW API: Limiting the maximum number of calls of subexp-call
- NEW API: ONIG_OPTION_NOT_BEGIN_STRING / NOT_END_STRING /
  NOT_BEGIN_POSITION
- Fixed behavior of ONIG_OPTION_NOTBOL / NOTEOL
- Fixed many problems found by OSS-Fuzz
- Fixed many problems found by Coverity
- Fixed CVE-2020-26159